Prevent using functions from the global scope with es6 (#5596)

* Prevent using functions from the global scope with es6

* check against static _dragging as requested by perliedman

src/control/Control.Layers.js

@@ -245,7 +245,7 @@ export var Layers = Control.extend({
 		});
 
 		if (this.options.sortLayers) {
-			this._layers.sort(L.bind(function (a, b) {
+			this._layers.sort(Util.bind(function (a, b) {
 				return this.options.sortFunction(a.layer, b.layer, a.name, b.name);
 			}, this));
 		}

src/dom/Draggable.js

@@ -75,7 +75,7 @@ export var Draggable = Evented.extend({
 
 		// If we're currently dragging this draggable,
 		// disabling it counts as first ending the drag.
-		if (L.Draggable._dragging === this) {
+		if (_dragging === this) {
 			this.finishDrag();
 		}